In the semi in vitro system for the synthesis of a specific protein ovalbumin a regulatory function of tRNA has been revealed for the first time by us. The ease of penetration of regulatory macromolecules into metazoan cells has implications on immigration of such molecules during differentiation and neoplastic transformation. To identify the tRNA(s) which control ovalbumin synthesis we developed during the past year an in vitro system of synthesizing ovalbumin which is completely tRNA dose dependent. To our knowledge this is the first such system perfected. With this system we plan to test the effectiveness of various tRNA fractions as potentiators or inhibitors of specific protein synthesis.